golomb: use unsigned arithmetics in svq3_get_ue_golomb()
This prevents undefined behaviour of signed left shift if the coded value is larger than 2^31. Large values are most likely invalid and caused errors or by feeding random. Validate every use of svq3_get_ue_golomb() and changed the place there the return value was compared with negative numbers. dirac.c was clean, fixed rv30 and svq3.
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